1. Field of the Invention
This invention relates generally to subsea water turbines and methods for extracting energy from ocean surface waves to generate electrical power and, more particularly, to a method using an underwater horizontal axis turbine apparatus supported on the seafloor completely submerged beneath ocean surface waves a distance from a coastline in an operating zone that straddles the division between an intermediate water zone and a shallow water zone where depths from the seafloor to the still water level are approximately in the range of 1/10th to 1/30th of prevailing wave lengths, wherein the turbine apparatus captures kinetic energy of vertically compressed orbital water particle motion for production of electrical power that is delivered to an onshore terminal.
2. Background Art
Mechanisms and methods for capture of ocean surface wave energy (tidal to wind driven frequencies) have been applied to human enterprise for centuries. In recent years emphasis has shifted to development of techniques that can capture the potential energy of wind waves (including swell) in locations where water depths are greater than one-half of the prevailing lengths of wave (known as “deep water”). The depth in these deep water zones is sufficient to avoid loss of potential energy of ocean surface waves due to interaction of the waves with the seafloor. The emerging techniques and systems convert undulations of the sea surface wave action (potential energy) into some form of kinetic energy that can be transformed into electrical energy. Most of the systems produce electrical power at the deep water site and use submarine cables to transmit the power ashore. Others use mechanical energy to pump seawater ashore to a revetment that creates enough hydraulic head for turbines to operate in outflow flumes. The techniques used to capture potential energy of waves are numerous and varied.
There are several patents and published applications directed toward various systems that produce power utilizing apparatus with floatation on or near the water surface. The assemblies are moved vertically by the potential energy of ocean waves which is transferred to electrical generators or other devices, located either on the floating body or under the water surface, to produce useful power for transmission to shore. The following are several examples: Carroll, U.S. Pat. No. 6,229,225; and Dempster, U.S. Patent Publication 2007/0108768.
There are several patents and published applications that disclose pivoting plates that are placed in the vicinity of the seafloor in an ocean and are operated by the reciprocating water mass beneath surface waves to produce power. The following are several examples: Kobashikawa, et al, U.S. Patent Publication 2004/0007881; Koivusaari, U.S. Patent Publication 2005/0066654; and Espedal, U.S. Patent Publication 2010/0111609.
There are several patents and published applications that disclose horizontal axis rotors and turbines having pivoting vanes or blades, airfoil shaped blades, and angularly disposed blades that are utilized to capture energy of a flowing water stream, ocean wave energy, or the reciprocating water mass beneath surface waves to produce power. The following are several examples: Geary, U.S. Pat. No. 6,006,518; Sauer, et al., U.S. Pat. No. 7,902,687; Siegel, U.S. Pat. No. 7,686,583; Lyatkher, U.S. Patent Publication 2009/0091134; and Hamner, U.S. Patent Publication 2010/0237626.
Stabins, U.S. Patent Publication 2009/0194997, discloses a horizontal axis Darrieus water wheel turbine having blades that may be straight or helical, and are held equidistant from the central rotating shaft by blade support members. The blades have an airfoil (Darrieus) cross section and are oriented so that a blade at its rotational apex moves directly opposite to the direction of water flow. The turbine is elevated such that the top portion, where blades travel directly against the direction of water flow, is in the air and above the water level.
Houlsby, et al., U.S. Patent Publication 2010/0284809, discloses a transverse flow water turbine having a horizontal axis. The rotor has a triangulated structure formed by at least three longitudinal blades having an airfoil (Darrieus) cross section supported between end plates along a line that is inclined with respect to the horizontal axis. The principal application envisaged for embodiments of the invention is to extract energy from tidal flows, but the device could equally be deployed in other types of flow, e.g. in rivers, or in flows caused by oceanic currents.
There are several patents and published applications that disclose rotors or turbines that are disposed inside an outer housing which is placed in a flowing water stream or beneath ocean surface waves wherein the housing channels the flowing water across the rotor or turbine to produce power. The following are examples: Farb, U.S. Patent Publication 2009/0243293; and Unno, U.S. Patent Publication 2010/0084862.
Tharp, U.S. Pat. No. 6,982,498, discloses an underwater hydro-electric farm comprising a plurality of electrical generator assemblies, each including a turbine blade/propeller assembly, arranged in a predetermined array on a bottom surface of a body of water within an ocean current path so that the turbine blade/propeller assemblies are caused to rotate as a result of being subjected to kinetic energy caused by the flow of an underwater current. Each of the electrical generator assemblies is removably secured in a cradle and is self contained and modular in configuration such that any of the electrical generator assemblies, including its coupled turbine blade/propeller assembly, is replaceable with another as a combined unit. Each of the electrical generator assemblies is in electrical communication with one another and connected via power transmission lines to a land based power converting facility.
Hydrokinetic turbines are also known that are designed to operate in unidirectional flowing waterways such as rivers, channels, and canals, As an example, Hydrovolts, Inc., of Seattle Wash., has developed several types of small water turbines with various blade configurations that are designed to capture hydrokinetic energy of swift moving unidirectional water flow in artificial waterways such as irrigation canals, that are tethered to the sides of the waterway to float at or near the water surface or to sit at the bottom of the canal. Use of these turbines for capturing the oscillatory water motion associated with surface waves is not disclosed or suggested.
The vertical axis Savonius rotor as a wind energy recovery device has long been used for high torque applications such as pumping water and grinding grain. The rotor unit is typically mounted on a vertical pipe or other support passing vertically through the center of the unit so that the unit revolves around the pipe when the wind blows onto the unit from any direction with sufficient velocity. Thus, the vertical axis Savonius rotor can use wind from any and all directions at all times. A two-bladed Savonius rotor typically operates at relatively low speeds in comparison to some other types of rotors and has usually been considered to be inefficient for electric generating purposes. A rotor that slows air down on one side while speeding it up on the other, as does the Savonius rotor, is subject to the Magnus-effect: lift produces a net transverse component of force on an immovable object or causes an untethered object to deflect from direction of the wind; the same phenomenon applies to a spinning baseball that curves during its flight toward homeplate.
Savonius, U.S. Pat. No. 1,766,765, discloses a vertical axis wind rotor having two oppositely arranged hollow shaped vanes of generally rectilinear generatrix formed by cylindrical, parabolic, helical or other suitable surfaces and arranged so that the inner edge of the vane extends to the segmental space bordered by the other vane, both vanes overlapping each other at their inner edges to form a gap for air passage adapted to force the air current from the hollow side of one vane to the hollow side of the other vane in an S-like path of substantially constant area. The vanes are provided with controllable outlet or inlet openings at places at which changes occur in the direction and one or more flaps on the circumference of the vane, which during normal operations adapt themselves to the curvature of the vanes, but when the rotor exceeds a predetermined speed are placed transversely to the face of the vane and thus uncover the passages, openings or ports for the stream of air. Use of these rotors for capturing the oscillatory water motion associated with surface waves is not disclosed or suggested.
When a Savonius rotor axis is set horizontally and tethered, “kiting” results due to the Magnus-effect. There are several water turbine patents that seek to produce power utilizing either vertical or horizontal axis Savonius type rotors. Most of these float on or near the water surface and are designed to operate in unidirectional flowing waterways such as rivers, channels, and canals. They operate on the principle of utilizing the velocity of the unidirectional flow for power output, rather than capturing the kinetic energy of reciprocating horizontal, vertical, and oblique components of vertically compressed generally elliptical orbit water particle motion beneath overhead ocean surface waves.
Russell, U.S. Pat. No. 6,172,429, discloses a hybrid energy recovery system for recovering energy from the natural and man-made sources of wind, water and sunshine by providing, within a given local area wind, water and solar apparatuses for simultaneously converting energy to produce electrical power from the combination of all three sources. The wind and water apparatuses comprise double speed Savonius rotor electrical generating apparatuses each of which includes two vertical axis Savonius type rotors mounted adjacent to one another for rotation about a common vertical axis with the blades of the rotor units being arranged so that the rotor units rotate in opposite directions relative to one another under the influence of a given wind. In the case of being powered by flowing water, the rotational axis of the rotor units is positioned horizontally with the water being discharged onto the rotor units from above the rotor units from a drain divided into two parts at its lower end to divide the flow of water into two parts each supplied to a respective one of the two rotor units.
Lagstrom, U.S. Patent Publication 2008/0116692, discloses arrangements for converting kinetic energy of ocean currents into electric energy, comprising a floating body carrying at least three longitudinally adjacent Savonius turbines, each of which has at least two blades with a substantially semicircular cross-section for transferring rotary motion of the turbine to an electric power generating unit. The floating body comprises elongated, mutually spaced and interconnected pontoons. One end of the pontoons is tapered inwardly to define a narrowed through-passage for water currents between the pontoons. In one embodiment, the Savonius turbines are suspended vertically across the through-passage so as to extend downwardly from an upper deck into the through-passage. Alternatively, the Savonius turbines are rotatably mounted at opposite ends in the pontoons so as to extend horizontally above each other across the through-passage.
Coman, U.S. Patent Publication 2007/0029806, discloses a floating electricity production unit for producing electricity by harvesting energy from unidirectional flowing water. A paddle wheel is stationarily positioned to penetrate the surface of a body of water, or a plurality of paddle wheels may be deployed on a single floating platform to optimize the transfer of the energy contained in the flow of water passing the floating platform. Water intensifiers having an angular surface are used to narrow the bounded cross section of the unidirectional flow impinging on the paddle wheels from the downstream floating platform. The paddlewheels and the water intensifiers would be incapable of operating in a reversing oscillatory water flow condition associated with the water particle motion beneath ocean surface waves.
The level of power output of turbines that are disposed in unidirectional flowing waterways such as rivers, channels, and canals, is directly related to flow velocity. There are several problems associated with turbines disposed in these locations. Although volumetric flow information may be available for a particular location, the water velocity varies from one potential site to another depending on the cross-sectional area of the waterway. The energy flow at the surface of a stream is higher than at the bottom. In a smooth channel, the water current is fastest at the center, but in a river the current flow varies depending upon the bottom geometry. Thus, the water velocity has a localized and site-specific profile, and location of the rotor dictates the amount of energy that can be produced. In a river, there are competing users of the water stream, such as boats, fishing vessels, bridges, etc., which may limit the effective usable area for a turbine installation. There may also be various types of suspended particles, debris, and materials, such as sand, rocks, and ice, in the waterway that could damage or adversely affect the operation of the turbine, as well as sea life in the vicinity that could raise environmental concerns or prohibit placement of a turbine in the waterway.